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Knee, George C.; Simmons, Stephanie; Gauger, Erik M.; Morton, John J. L.; Riemann, Helge; Abrosimov, Nikolai V.; Becker, Peter; Pohl, Hans-Joachim; Itoh, Kohei M.; Thewalt, Mike L. W.; Briggs, G. Andrew D.; Benjamin, Simon C. |
| Title |
Violation of a Leggett–Garg inequality with ideal non-invasive measurements |
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Journal Article |
| Year |
2012 |
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Nature Communications |
Abbreviated Journal |
Nat. Comm. |
| Volume |
3 |
Issue  |
606 |
Pages |
6 |
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fromIPMRAS |
| Abstract |
The quantum superposition principle states that an entity can exist in two different states simultaneously, counter to our 'classical' intuition. Is it possible to understand a given system's behaviour without such a concept? A test designed by Leggett and Garg can rule out this possibility. The test, originally intended for macroscopic objects, has been implemented in various systems. However to date no experiment has employed the 'ideal negative result' measurements that are required for the most robust test. Here we introduce a general protocol for these special measurements using an ancillary system, which acts as a local measuring device but which need not be perfectly prepared. We report an experimental realization using spin-bearing phosphorus impurities in silicon. The results demonstrate the necessity of a non-classical picture for this class of microscopic system. Our procedure can be applied to systems of any size, whether individually controlled or in a spatial ensemble. |
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767 |
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Wu, Ming C. |
| Title |
Optoelectronic tweezers |
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Journal Article |
| Year |
2011 |
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Nature Photonics |
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Nature Photon |
| Volume |
5 |
Issue |
6 |
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322-324 |
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fromIPMRAS |
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Using projected light patterns to form virtual electrodes on a photosensitive substrate, optoelectronic tweezers are able to grab and move micro- and nanoscale objects at will, facilitating applications far beyond biology and colloidal science. |
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775 |
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Fazal, Furqan M.; Block, Steven M. |
| Title |
Optical tweezers study life under tension |
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Journal Article |
| Year |
2011 |
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Nature Photonics |
Abbreviated Journal |
Nat. Photon. |
| Volume |
5 |
Issue |
6 |
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318-321 |
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fromIPMRAS |
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Optical tweezers have become one of the primary weapons in the arsenal of biophysicists, and have revolutionized the new field of single-molecule biophysics. Today's techniques allow high-resolution experiments on biological macromolecules that were mere pipe dreams only a decade ago. |
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776 |
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Bialczak, R. C.; Ansmann, M.; Hofheinz, M.; Lucero, E.; Neeley, M.; O'Connell, A. D.; Sank, D.; Wang, H.; Wenner, J.; Steffen, M.; Cleland, A. N.; Martinis, J. M. |
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Quantum process tomography of a universal entangling gate implemented with Josephson phase qubits |
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Journal Article |
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2010 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
| Volume |
6 |
Issue |
6 |
Pages |
409-413 |
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fromIPMRAS |
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Quantum gates must perform reliably when operating on standard input basis states and on complex superpositions thereof. Experiments using superconducting qubits have validated truth tables for particular implementations of, for example, the controlled-NOT gate, but have not fully characterized gate operation for arbitrary superpositions of input states. Here we demonstrate the use of quantum process tomography (QPT) to fully characterize the performance of a universal entangling gate between two superconducting qubits. Process tomography permits complete gate analysis, but requires precise preparation of arbitrary input states, control over the subsequent qubit interaction and ideally simultaneous single-shot measurement of output states. In recent work, it has been proposed to use QPT to probe noise properties and time dynamics of qubit systems and to apply techniques from control theory to create scalable qubit benchmarking protocols. We use QPT to measure the fidelity and noise properties of an entangling gate. In addition to demonstrating a promising fidelity, our entangling gate has an on-to-off ratio of 300, a level of adjustable coupling that will become a requirement for future high-fidelity devices. This is the first solid-state demonstration of QPT in a two-qubit system, as QPT has previously been demonstrated only with single solid-state qubits. |
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RPLAB @ gujma @ |
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803 |
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Crespi, Andrea; Ramponi, Roberta; Osellame, Roberto; Sansoni, Linda; Bongioanni, Irene; Sciarrino, Fabio; Vallone, Giuseppe; Mataloni, Paolo |
| Title |
Integrated photonic quantum gates for polarization qubits |
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Journal Article |
| Year |
2011 |
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Nature Communications |
Abbreviated Journal |
Nat. Comm. |
| Volume |
2 |
Issue |
566 |
Pages |
6 |
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fromIPMRAS |
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The ability to manipulate quantum states of light by integrated devices may open new perspectives both for fundamental tests of quantum mechanics and for novel technological applications. However, the technology for handling polarization-encoded qubits, the most commonly adopted approach, is still missing in quantum optical circuits. Here we demonstrate the first integrated photonic controlled-NOT (CNOT) gate for polarization-encoded qubits. This result has been enabled by the integration, based on femtosecond laser waveguide writing, of partially polarizing beam splitters on a glass chip. We characterize the logical truth table of the quantum gate demonstrating its high fidelity to the expected one. In addition, we show the ability of this gate to transform separable states into entangled ones and vice versa. Finally, the full accessibility of our device is exploited to carry out a complete characterization of the CNOT gate through a quantum process tomography. |
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